Why is my ex mad at me when he dumped me?

Long story short, my ex boyfriend broke up with me last year saying that he wasn't looking for a relationship. I accepted it and we somehow still kept in touch through text messages and fb. The other day, he texted me saying that he was going to move abroad and work. He then started asking me questions as to when I was going to graduate, what my future plans were etc. Then he said that he was sad to be leaving me, that he wished he could have someone to come with him and share his journey but that unfortunately life wasn't that simple.

I agreed with him and told him that I was sad too that he was leaving, but told him that I wished him all the best on his journey and that I was sure that he would be fine etc. He simply replied with "That's true..."

A week later and he's started posting about how terrible of a girlfriend I was, how his life will be so much better without me and that he's moved on. I haven't responded to anything and just ignored the whole ordeal.

But why is he angry at me when he tells me that he's leaving? I can't exactly do anything for him considering the fact, that he dumped me.

Well if him acting this way doesn't show you what a jerk he really is, then I don't know what will. The best revenge is never giving him even a second of your time ever again. Not even a text to say you are done with him. Nothing. Trust me, it will drive him crazy.